If you ever need to look up an ASCII code, say for an HTML entity such as a © or ® symbol, you can simply use the CODE command in Excel:
This returns a value of 169, so your HTML code would be: ©
It's easy to make your own ASCII chart in Excel. Just select cells in a column at least down to 266 and use Fill, Series on the Home menu to number them from 1 to 255:
Now in the next column over next to the "1" in your ASCII code column, enter:
Now fill this down to finish your chart:
The ASCII code 1 (along with many other codes) won't show any value, and not every ASCII code will work as an HTML entity. But you'll find many useful codes including the ° degrees sign (°), ¥ Yen symbol (¥) and all sorts of accents for different languages.